OBJECTIVEGoal of this study was to test the potential regulatory effects of Vpr on Vif and Vif-mediated degradation of APOBEC3G.

METHODSThe Vpr effect was first tested in a fission yeast RE007 strain that carries a single integrated copy of vpr gene in the chromosome and transformed with a vif-expressing plasmid. Similar tests were also carried out in a muristerone A vpr-inducing HEK293 mammalian cell line that were transfected with the plasmids expressing vif and/or APOBEC3G. Western Blot analyses were used to measure the corresponding protein levels under different experimental conditions.

RESULTSExpression of HIV-1 vpr appears to enhance the protein levels of Vif both in fission yeast and mammalian cells. A similar enhancement effect of APOBEC3G by Vpr was also detected in mammalian cells. Interestingly, however, the increased Vif protein level by Vpr did not result in more APOBEC3G degradation than without Vpr, indicating a potential regulatory effect of Vpr on Vif-mediated proteolysis of APOBEC3G.

CONCLUSIONTo our knowledge, this is the first report describing a potentially conserved and regulatory effect of HIV-1 Vpr on Vif and Vif-mediated protein degradation of APOBEC3G.

APOBEC-3G Deaminase ; Animals ; Cell Line ; Cytidine Deaminase ; biosynthesis ; metabolism ; Gene Expression ; Gene Products, vif ; biosynthesis ; metabolism ; Gene Products, vpr ; metabolism ; HIV-1 ; Humans ; Schizosaccharomyces ; genetics

OBJECTIVETo observe the inhibitory effect of a replication-defective hepatitis B virus (HBV) vector plasmid expressing A3C on HBV replication in vitro.

METHODSThe HBV vector plasmisd pCH-LJ3-A3C and pCH-LJ3-hrGFP expressing A3C and hrGFP were constructed using PCR and gene recombination technique. The two recombinant plasmids were separately cotranfected into HepG2 cells along with the wild-type HBV plasmid pCH-3093. The HBV DNA in the cell cytoplasmic lysates and in the cell culture supernatant was extracted for Southern blotting, and the nucleocapsid-associated HBV DNA were amplified by PCR, cloned and sequenced.

RESULTSpCH-LJ3-A3C showed obvious inhibitory effect on HBV DNA in the cytoplasmic lysates and cell culture supernatant, causing a reduction of the HBV DNA by 31% and 40%, respectively. The pCH-LJ3-A3C plasmid was capable of editing the HBV DNA. Among the 50 sequenced clones, 36 clones had G-A mutations, with a total of 982 such mutations.

CONCLUSIONpCH-LJ3-A3C can inhibit the replication of HBV primarily by editing HBV DNA. The pCH-LJ3-A3C plasmid may serve as a new antiviral agent against human HBV infection.

APOBEC-3G Deaminase ; Antiviral Agents ; pharmacology ; Base Sequence ; Cytidine Deaminase ; genetics ; metabolism ; Genetic Vectors ; genetics ; Hep G2 Cells ; Hepatitis B virus ; genetics ; physiology ; Humans ; Molecular Sequence Data ; Plasmids ; genetics ; metabolism ; RNA, Messenger ; genetics ; metabolism ; Virus Replication ; genetics

Apolipoprotein B mRNA-editing enzyme catalytic polypeptide 3 protein G (APOBEC3G) is part of the innate immune system of host cells and has cytidine deaminase activity. It specifically incorporates into the virion during HIV-1 replication. The incorporation of APOBEC3G needs its interaction with HIV-1 Gag. In the HIV-1 reverse transcription process, APOBEC3G deaminates dC to dU in the first minus strand cDNA, and then induces extensive hypermutation in the viral genome. Besides deamination, APOBEC3G also inhibits HIV-1 by some kinds of non-deamination mechanisms which need to be further elucidated. HIV-1 Vif counteracts the activity of APOBEC3G by an ubiquitin-proteasome-mediated degradation of APOBEC3G. As a broad spectrum inhibitor of viruses, APOBEC3G also inhibits various retroviruses, retrotransposons and other viruses like HBV. Upregulating the expression of APOBEC3G or blocking the Vif-mediated degradation of APOBEC3G might be novel strategies to treat HIV-1 infection in the future.
APOBEC-3G Deaminase ; Amino Acid Substitution ; Anti-HIV Agents ; metabolism ; Cytidine Deaminase ; genetics ; metabolism ; Gene Expression ; HIV Infections ; metabolism ; HIV-1 ; genetics ; physiology ; Humans ; Virus Replication ; vif Gene Products, Human Immunodeficiency Virus ; genetics ; metabolism

APOBEC3 is a class of cytidine deaminase, which is considered as a new member of the innate immune system, and APOBEC3G belongs to this family. The research about APOBEC3G is a new direction of innate immune defense mechanism against virus. APOBEC3G has the restrictive activity on many viral replications, which deaminates dC to dU in the viral genome and then induces extensive hypermutation. APOBEC3G can also interrupt viral replication at several phases such as reverse transcription, replication, nucleocapsid and so on by non-deamination mechanisms. However, virus can encode viral proteins to counteract the restriction activity of APOBEC3G. Elucidation of the antagonistic interaction between APOBEC3G and the virus will be contributed to development of new antiviral drugs in the future.
APOBEC-3G Deaminase ; Animals ; Cytidine Deaminase ; genetics ; metabolism ; DNA Replication ; Deamination ; HIV-1 ; physiology ; Hepacivirus ; genetics ; physiology ; Hepatitis B virus ; genetics ; physiology ; Humans ; Paramyxoviridae ; genetics ; physiology ; Retroviridae ; physiology ; Virus Replication ; vif Gene Products, Human Immunodeficiency Virus ; metabolism

OBJECTIVETo investigate the effect of apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G (APOBEC3G) mediated antiviral activity against hepatitis B virus (HBV) and duck hepatitis B virus (DHBV).

METHODSTotal RNA was extracted from peripheral blood mononuclear cells (PBMCs), RT-PCR product was cloned into the EcoR I/Hind III restriction sites of the CMV-driven expression vector fused with a hemagglutinin fusion epitope tag at its carboxyl terminal. Replication competent 1.3 fold over-length HBV was constructed with full-length HBV of ayw subtype. The mammalian hepatoma cell HepG2 was cotransfected with the replication competent 1.3 fold over-length HBV and various amounts of CMV-driven expression vector encoding APOBEC3G-HA. Levels of HBsAg and HBeAg in the media of the transfected cells were determined by ELISA, HBV DNA. RNA from intracellular core particles was examined using Northern and Southern blot analyses. Chicken hepatoma cell LMH was cotransfected with head-to-tail dimer of an EcoR I monomer of DHBV and various amounts of CMV-driven expression vector encoding APOBEC3G-HA. DHBV DNA from intracellular core particles was examined using Southern blot analysis.

RESULTSCMV-driven expression vector encoding APOBEC3G-HA and replication competent 1.3 fold over-length HBV were constructed. There was a dose dependent decrease in the levels of intracellular core-associated viral (HBV and DHBV) DNA and extracellular production of HBsAg and HBeAg. Levels of intracellular core-associated viral RNA were also decreased, but the expression of HBcAg remained almost unchanged.

CONCLUSIONAPOBEC3G suppresses HBV and DHBV replication and also suppresses HBsAg and HBeAg expression.

APOBEC-3G Deaminase ; Cytidine Deaminase ; genetics ; Hep G2 Cells ; Hepatitis B Surface Antigens ; metabolism ; Hepatitis B Virus, Duck ; physiology ; Hepatitis B e Antigens ; metabolism ; Hepatitis B virus ; physiology ; Humans ; RNA, Messenger ; genetics ; Virus Replication

Human immunodeficiency virus type 1 (HIV-1) viral infectivity factor (Vif), one of the accessory proteins, which is a small basic phosphoprotein, is essential for viral replication and pathogenesis. The best well-characterized function of Vif is its ability to neutralize the host cell antiviral factor, apolipoprotein B mRNA editing enzyme catalytic polypeptide like 3G (APOBEC3G), which makes the viral particles more infective. In addition, Vif can regulate the reverse transcription and the advanced stage of replication of the virus particle, as well as induce the termination of cell cycle at G2 stage and so on. The designed drug aimed directly at Vif can efficiently block the maturation and infectivity of HIV-1. In this review, the structure, function and especially the related inhibitors of Vif are reviewed.
APOBEC-3G Deaminase ; Amino Acid Sequence ; Anti-HIV Agents ; pharmacology ; Cytidine Deaminase ; metabolism ; Ethylenediamines ; pharmacology ; HIV-1 ; physiology ; Humans ; Reverse Transcription ; Virus Replication ; vif Gene Products, Human Immunodeficiency Virus ; antagonists & inhibitors ; genetics ; metabolism ; physiology

Apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G (APOBEC3G) cDNA was amplified from total RNA prepared from nonpermissive H9 cells by RT-PCR. APOBEC3G cDNA is 1155nt long, encoding 384 amino acids. The APOBEC3G gene was then cloned into the eukaryotic expression vector pEGFP-C3. The generated pEGFP-3G construct was then transfected into CD4+ HeLa cell to determine the expression and the subcellular localization of GFP-APOBEC3G fusion protein. Under CLSM the localization of the expressed GFP-APOBEC3G in the cytoplasm of CD4+ HeLa cells was observed.
APOBEC-3G Deaminase ; Cell Line ; Cytidine Deaminase ; Cytoplasm ; metabolism ; DNA, Complementary ; genetics ; isolation & purification ; metabolism ; Green Fluorescent Proteins ; genetics ; metabolism ; HeLa Cells ; Humans ; Microscopy, Confocal ; methods ; Nucleoside Deaminases ; genetics ; metabolism ; Recombinant Fusion Proteins ; genetics ; metabolism ; Repressor Proteins ; genetics ; metabolism ; Reverse Transcriptase Polymerase Chain Reaction

Activation-induced cytidine deaminase (AID) is required for the generation of antibody diversity through initiating both somatic hypermutation (SHM) and class switch recombination. A few research groups have successfully used the feature of AID for generating mutant libraries in directed evolution of target proteins in B cells in vitro. B cells, cultured in suspension, are not convenient for transfection and cloning. In this study, we established an AID-based mutant accumulation and sorting system in adherent human cells. Mouse AID gene was first transfected into the human non-small cell lung carcinoma H1299 cells, and a stable cell clone (H1299-AID) was selected. Afterwards, anti-hTNF-α scFv (ATscFv) was transfected into H1299-AID cells and ATscFv was displayed on the surface of H1299-AID cells. By 4-round amplification/flow cytometric sorting for cells with the highest affinities to hTNF-alpha, two ATscFv mutant gene clones were isolated. Compared with the wild type ATscFv, the two mutants were much more efficient in neutralizing cytotoxicity of hTNF-alpha. The results indicate that directed evolution by somatic hypermutation can be carried out in adherent non-B cells, which makes directed evolution in mammalian cells easier and more efficient.
Animals ; Antibody Affinity ; Cells, Cultured ; Cytidine Deaminase ; genetics ; metabolism ; HEK293 Cells ; Humans ; Immunoglobulin Variable Region ; genetics ; immunology ; Mice ; Mutation ; Single-Chain Antibodies ; chemistry ; genetics ; immunology ; Somatic Hypermutation, Immunoglobulin ; genetics ; immunology ; Tumor Necrosis Factor-alpha ; immunology

OBJECTIVETo study the expression level and intracellular localization of APOBEC3G in peripheral blood mononuclear cells (PBMCs) and liver tissues of chronic HBV patients.

METHODSThe expression level and intracellular localization of APOBEC3G in PBMCs and liver tissues were detected using the western blot and confocal laser scanning microscope (CLSM).

RESULTSWestern-blot showed that the expression level of APOBEC3G in PBMCs of healthy controls was very low. The relative expression levels of APOBEC3G in PBMC of patients with chronic hepatitis B, chronic severe hepatitis, liver cirrhosis, or liver cancer were 4.12+/-0.21, 4.07+/-0.28, 4.16+/-0.36 or 4.21+/-0.39 respectively, which were higher than that in the healthy controls. However, there was no significant difference in APOBEC3G expression among different chronic HBV patients (q = 0.931, 0.744, 1.675, 1.675, 2.606 or 0.931, respectively, all P values more than 0.05). In addition, there was no significant difference on APOBEC3G in liver tissues between chronic hepatitis B patients and hepatocellular carcinoma patients (4.40+/-0.34 vs 4.34+/-0.43, q = 0.588, P more than 0.05). CLSM indicated that the localization of APOBEC3G protein was in cytoplasm of PBMCs and hepatocytes.

CONCLUSIONAPOBEC3G is upregulated in the PBMCs of chronic hepatitis B patients.

APOBEC-3G Deaminase ; Blotting, Western ; Case-Control Studies ; Cytidine Deaminase ; genetics ; metabolism ; Cytoplasm ; metabolism ; Hepatitis B, Chronic ; metabolism ; pathology ; virology ; Humans ; Leukocytes, Mononuclear ; metabolism ; Liver ; metabolism ; pathology ; Liver Cirrhosis ; metabolism ; pathology ; virology ; Liver Neoplasms ; metabolism ; pathology ; virology ; Microscopy, Confocal ; methods ; RNA, Messenger ; genetics ; metabolism

Targeted point mutagenesis through homologous recombination has been widely used in genetic studies and holds considerable promise for repairing disease-causing mutations in patients. However, problems such as mosaicism and low mutagenesis efficiency continue to pose challenges to clinical application of such approaches. Recently, a base editor (BE) system built on cytidine (C) deaminase and CRISPR/Cas9 technology was developed as an alternative method for targeted point mutagenesis in plant, yeast, and human cells. Base editors convert C in the deamination window to thymidine (T) efficiently, however, it remains unclear whether targeted base editing in mouse embryos is feasible. In this report, we generated a modified high-fidelity version of base editor 2 (HF2-BE2), and investigated its base editing efficacy in mouse embryos. We found that HF2-BE2 could convert C to T efficiently, with up to 100% biallelic mutation efficiency in mouse embryos. Unlike BE3, HF2-BE2 could convert C to T on both the target and non-target strand, expanding the editing scope of base editors. Surprisingly, we found HF2-BE2 could also deaminate C that was proximal to the gRNA-binding region. Taken together, our work demonstrates the feasibility of generating point mutations in mouse by base editing, and underscores the need to carefully optimize base editing systems in order to eliminate proximal-site deamination.
APOBEC-1 Deaminase ; genetics ; metabolism ; Animals ; Bacterial Proteins ; genetics ; metabolism ; Base Sequence ; CRISPR-Associated Protein 9 ; CRISPR-Cas Systems ; Cytidine ; genetics ; metabolism ; Embryo Transfer ; Embryo, Mammalian ; Endonucleases ; genetics ; metabolism ; Gene Editing ; methods ; HEK293 Cells ; High-Throughput Nucleotide Sequencing ; Humans ; Mice ; Mice, Inbred C57BL ; Microinjections ; Plasmids ; chemistry ; metabolism ; Point Mutation ; RNA, Guide ; genetics ; metabolism ; Thymidine ; genetics ; metabolism ; Zygote ; growth & development ; metabolism ; transplantation